Download 06.Notes-2010-MillikansOilDrop

Millikan’s Oil Drop Experiment
Introduction:
http://www.youtube.com/watch?v=91E6KvCvRf0
http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/004_MILLIKANOIL.MOV
http://dev.physicslab.org/Document.aspx?doctype=3&filenme=AtomicNuclear_MillikanOilDrop.xml
Big Ideas:
1. What was the charge (positive, negative, or neutral) on Millikan’s oil drop after he sprayed them
from an atomizer? Why?
2. When the oil droplets were sprayed into an electric field, they experienced a force. Which direction
must the electric force on the oil drops be in order to oppose the force of gravity on the drops?
3. Which plate must be on top of the oil drops for the electric force to oppose the force of gravity?
4. Finish this picture by drawing in the charge on each plate (top and bottom) and a free body diagram
on the oil drop.
4. What did Millikan’s experiment allow him to calculate?
5. What does it mean that charge is “quantized”?
EXAMPLE #1
Go to: http://physics.wku.edu/~womble/phys260/millikan.html
The very simplistic simulation shows red oil drops with mass of 1x10 -15 kg in an electric field. Adjust
the Electric Field Intensity until you get the drops to hover. Use your Electric Field Intensity to
calculate an experimental value of the charge of an electron.
EXAMPLE #2
In a Millikan oil drop experiment, a drop has been found to have a mass of 2x10 –16 kg . When the
electric field is 2465 N/C, the drop is suspended motionless.
a. What is the charge on the oil drop?
b. How many excess electrons does this mean the oil drop has?
EXAMPLE #3
In a different Millikan oil drop experiment, a drop has been found to weigh 1.9x10-14 N. When the
electric field is 4.0x104 N/C, the drop is suspended motionless.
a. What is the charge on the oil drop?
b. How many excess electrons does this mean the oil drop has?